Synthesis and catalytic activity of rhodium diene complexes bearing indenyl-type fullerene η5-ligand

Article abstract of DOI:10.1016/S0022-328X(03)00465-0

Rhodium η⁵-complexes bearing an indenyl-type fullerene ligand, Rh[C₆₀(PhCH₂)₂Ph](cod) (2), Rh[C₆₀(PhCH₂)₂Ph](nbd) (3) and Rh(C₇₀Ph₃)(cod) (4), have been synthesized from the corresponding fullerene tri-adducts in 93-96% yields. X-ray crystallographic analysis of 4 indicated that the structure of 4 is similar to that of Rh(Ind)(cod). The rhodium complex 2 catalyzes alkyne trimerization reactions and hydroboration reactions.

Full text of DOI:10.1016/S0022-328X(03)00465-0

Journal of Organometallic Chemistry 683 (2003) 295Á300
/
www.elsevier.com/locate/jorganchem
Synthesis and catalytic activity of rhodium diene complexes bearing
indenyl-type fullerene h5-ligand
Motoki Toganoh, Yutaka Matsuo, Eiichi Nakamura *
Department of Chemistry, The University of Tokyo, Bunkyo-Ku, Hongo 7-3-1 Tokyo, Japan
Received 4 March 2003; received in revised form 9 May 2003; accepted 16 May 2003
Abstract
Rhodium h5-complexes bearing an indenyl-type fullerene ligand, Rh[C60(PhCH2)2Ph](cod) (2), Rh[C60(PhCH2)2Ph](nbd) (3) and
Rh(C70Ph3)(cod) (4), have been synthesized from the corresponding fullerene tri-adducts in 93Á96% yields. X-ray crystallographic
/
analysis of 4 indicated that the structure of 4 is similar to that of Rh(Ind)(cod). The rhodium complex 2 catalyzes alkyne
trimerization reactions and hydroboration reactions.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Fullerene; Rh complex; Indenyl ligand; Catalysis
1. Introduction
We previously reported a regioselective synthesis of
fullerene tri-adducts, C60R3H and C70R3H [1,2]. Thus,
treatment of 1,7-diorgano[60]fullerene [3] with
a
Grignard reagent affords, after hydrolysis and HPLC
purification, the [60]fullerene tri-adduct C60R3H in good
yield, and treatment of [70]fullerene with an organo-
copper reagent gives, after aqueous work up, the
[70]fullerene tri-adduct C70R3H in quantitative yield.
Both compounds were easily converted to the corre-
sponding potassium complexes, K(C60R3) and
K(C70R3), by treatment with t-BuOK in THF at
ambient temperature. Theoretical studies on the model
compounds K(C60H3) and K(C70H3) revealed that the
structural as well as electronic properties of the indenyl
moiety embedded in the extensive p-electron conjuga-
tion of the fullerene sphere is similar to those of a simple
indenyl ligand. One can therefore expect to synthesize
their transition metal complexes. We wish to report here
the synthesis of rhodium diene complexes bearing the
indenyl-type fullerene ligands. Catalytic activity of such
a complex will also be briefly discussed.
2. Results and discussion
In the C60R5 metal h5-cyclopentadienyl complexes
that we reported previously [4,5], the five R groups
surround the metal center, leaving little free space
between them and the metal atom. Likely owing to
this effect, we could not synthesize rhodium diene
complexes such as Rh(C60Me5)(cod) (codꢀ
/
1,5-cyclooc-
* Corresponding author.
tadiene), which we expected to be useful for catalysis [6Á
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00465-0

296
M. Toganoh et al. / Journal of Organometallic Chemistry 683 (2003) 295Á300
/
8]. We therefore considered that the less sterically
encumbered C60R3 and C70R3 ligands would give us
more flexibility in the synthesis of h5-transition metal
complexes of fullerenes.
Unlike the C60R5 ligand (note that we could only
synthesize a Rh dicarbonyl complex) [5], the C60R3
ligand readily formed the desired rhodium complexes by
simple transmetallation strategy. Thus, treatment of
C60(PhCH2)2PhH (1, a near 3:2 mixture of regioisomers
as shown) with t-BuOK (1.2 equivalent) in THF at
25 8C caused an immediate color change from brown to
dark green, suggesting generation of the corresponding
potassium complex K[C60(PhCH2)2Ph] [1]. 1H-NMR
analysis in THF-d8 showed that the isomeric mixture
Fig. 1. Molecular structure of 4.
of
1 gave a single product, K[C60(PhCH2)2Ph].
[RhCl(cod)]2 (2.0 equivalent) was then added to this
green solution in one portion. HPLC analysis on the
reaction mixture indicated that the reaction was rapid,
completing within 45 min. The crude product was
isolated as dark green powder by precipitation with
hexane. After washing and air-drying overnight,
Rh[C60(PhCH2)2Ph](cod) (2) was obtained in 93% yield
(Scheme 1) as a single product. The rhodium complex 2
is stable and easy to handle: it remains stable for a few
months in air under ambient light. Support for the
assigned C1 symmetric structure of 2 came from the
HRMS, H-NMR, and 13C-NMR data. The H-NMR
spectrum shows four distinct doublet peaks at d 4.05,
4.19, 4.74, 4.84 ppm due to the methylene groups of the
benzyl addends, multiplet peaks between d 2.22 and 2.32
ppm and between d 2.50 and 2.72 ppm due to the
methylene groups of the 1,4-cyclooctadiene ligand, and
multiplet peaks between d 4.65 and 4.73 ppm and
between d 5.40 and 5.48 ppm due to the protons
attached to the sp2 carbon atoms of the 1,4-cycloocta-
diene ligand. The 13C-NMR spectrum shows two
doublet peaks due to the sp2 carbon atoms of the 1,4-
cyclooctadiene ligand at d 74.73 and 74.92 ppm, which
are coupled with the rhodium atom with coupling
1
constants of JRhÃC
similar reaction with [RhCl(nbd)]2 (nbdꢀ
ꢀ
/
12.5 and 13.3 Hz, respectively. A
norbona-
/
diene) afforded Rh[C60(PhCH2)2Ph](nbd) (3) in 96%
yield as a single product.
We also synthesized a rhodium h5-complex from the
indenyl-type [70]fullerene ligand. The metathesis reac-
tion of K(C70Ph3) [2] with [RhCl(cod)]2 gave the desired
dark-brown rhodium complex Rh(C70Ph3)(cod) (4) in
94% yield as single product (Eq. (1)). The HRMS and
1H-NMR spectra are fully consisted with the assigned
Cs symmetric structure. X-ray crystallographic analysis
proved the molecular structure that we propose for 4.
Slow diffusion of hexane into a CS2 solution of 4 gave
black thin plates, one of which was analyzed by X-ray
diffraction. The ORTEP drawing and space-filling models
are shown in Fig. 1. One can see in the top view some
free space around the metal center, which may allow fast
ligand exchange required in catalysis. The structure
around the rhodium metal shares some feature with
that of Rh(Ind)(cod) (5) [9]. For example, lengths of the
1
1
˚ ˚
cod bonds (avg. 4: 2.149 A, 5: 2.127 A) and the
RhÃ
/
˚
indenyl bonds (avg. 4: 2.317 A, 5:
lengths of the RhÃ
/
˚
2.282 A) are similar to each other.
ð1Þ
Scheme 1. Synthesis of rhodium complexes bearing the
(PhCH2)2PhC60 ligand.

M. Toganoh et al. / Journal of Organometallic Chemistry 683 (2003) 295Á
/
300
297
Table 1
Alkyne trimerization reaction catalyzed by 2
fullerene ligand is responsible for the change of the
selectivity, and this issue will be subject of further
studies.
Starting with the indenyl-type fullerene h5-ligands, we
have synthesized a new class of rhodium diene com-
plexes, which have not so far been obtainable from the
more hindered C60R5 ligand. The rhodium complex
exhibited a considerable catalytic activity in the alkyne
trimerization and the hydroboration reactions, where we
obtained a sign of favorable effects of the use of the
fullerene ligand system. Given the various new possibi-
lities of the fullerene cyclopentadienyl ligand systems
[12], we expect that the indenyl ligands and their
transition metal complexes will offer exciting new
opportunities for chemists in the field of organic
synthesis, catalysis, and nano-science.
3. Experimental
3.1. General procedures
The rhodium complexes thus obtained show consider-
able catalytic activity in an alkyne trimerization reaction
[10]. The complex 2 was examined, since it shows the
highest solubility among the rhodium complexes synthe-
sized in the present studies (Table 1). When dimethyl
acetylenedicarboxylate was treated with 2 (1.0 mol.%) in
1,2-dichlorobenzene at 60 8C for 1 d, hexa(methoxycar-
bonyl)benzene was obtained in 99% isolated yield.
Tri(methoxycarbonyl)triphenylbenzene and hexaphe-
nylbenzene were also obtained albeit in low yields. The
catalytic activity and regioselectivity of 2 in alkyne
trimerization reactions is comparable to that of 5 [7].
The rhodium complex 2 also catalyzes hydroboration
reaction (Scheme 2) [11]. When 4-(benzyloxy)cyclohex-
ene was treated with catecholborane (3.6 equivalent) in
the presence of a catalytic amount of 2 (1.7 mol.%) in
THF for 3 d at 25 8C, hydroboration products were
obtained in 70% yield as a mixture of four isomers as
shown. It is notable that the fullerene complex exhibits a
All reactions were carried out in an oven-dried
reaction vessel under argon or nitrogen and were
analyzed by HPLC (column: Buckyprep, 4.6ꢁ
mm, Nacalai tesque; flow rate: 1.0 ml minꢂ1; eluent:
toluene/2-propanolꢀ7/3; detector: SPD-M10Avp, Shi-
/
250
/
1
madzu). All H-NMR spectra were taken at 400 MHz
(JEOL EX-400 and AL400), and 13C-NMR spectra at
100 MHz. Spectra are reported in part per million from
internal tetramethylsilane or the residual protons of the
1
deutrated solvent for the H-NMR spectra, and from
the deutrated solvent for the 13C-NMR spectra. IR
spectra were recorded on an Applied Systems Inc.,
REACT IR 1000 instrument as powders on a diamond
probe; absorptions are reported in cmꢂ1. Mass spectra
were measured with a Shimadzu LCMS-QP8000 instru-
ment (APCI mode) equipped with a Buckyprep column.
High resolution mass spectra were recorded on a JEOL
JMS-T100LC machine.
product selectivity different from that of
a
Rh(Ind)(C2H4)2 catalyst [8], favoring the formation of
the 1,4-isomers and of the trans isomers as shown in
Scheme 2. It seems likely that the steric effect of the
3.2. Solvents and materials
All commercially available reagents were distilled or
recrystallized before use unless otherwise noted. THF
was purchased from KANTO KAGAKU and stored
over MS4A under nitrogen. 1,2-Dichlorobenzene was
distilled from CaH2 and dried over MS4A. The water
content of the solvents was determined each time with a
Karl-Fischer moisture titrator (MK-210, Kyoto Elec-
tronics Company) to be less than 20 ppm.
C60(PhCH2)2PhH and C70Ph3H were prepared in a
reported manner [1,2]. A solution of t-BuOK in THF
(1 M) was purchased from Sigma Aldrich Japan K.K.
and used as received.
Scheme 2. Hydroboration reaction catalyzed by 2.

298
M. Toganoh et al. / Journal of Organometallic Chemistry 683 (2003) 295Á300
/
3.3. Synthesis of [(1,2,3,4,5-h)-6,9-dibenzyl-12-phenyl-
9,12-dihydro(C60-Ih)[5,6]fulleren-1(6H)-yl](h2,h2-1,4-
cyclooctadiene)rhodium(I) ŽRh[C60(PhCH2)2Ph](cod)
(2)
13.2 Hz, 1H), 4.86 (d, Jꢀ
5H), 7.61Á7.77 (m, 4H), 7.81Á
(m, 2H), 8.25Á
8.31 (m, 2H); 13C-NMR (toluene-d8, 100
/
13.2 Hz, 1H), 7.38Á
/
7.52 (m,
/
/
7.87 (m, 2H), 7.93Á
/8.00
/
MHz) d 47.71, 48.58, 49.60, 50.04, 50.80, 50.91, 53.94,
55.89, 57.11, 58.06, 60.22, 61.06, 82.87, 102.08, 127.28,
127.45, 127.81, 128.05, 128.48, 128.95, 129.19, 130.86,
131.31, 136.00, 136.23, 137.04, 139.47, 140.35, 142.34,
142.48, 142.78, 142.75, 142.98, 143.12, 143.24, 143.47,
143.71, 143.93, 144.13, 144.18, 144.42, 144.51, 144.66,
144.72, 145.30, 145.37, 145.55, 145.65, 145.78, 145.92,
146.50, 146.59, 146.68, 146.91, 146.97, 147.21, 147.28,
147.34, 147.77, 147.95, 148.27, 148.43, 148.91, 149.03,
149.20, 149.38, 150.18, 150.23, 150.33, 150.44, 150.61,
150.87, 151.04, 156.58, 158.56; UV lmax 684, 375, 309
nm; HRMS (APCI-) Found: 1174.11690; Calc. for C87-
To a solution of C60(PhCH2)2PhH (1, 50.5 mg, 51.5
mmol) in 5.00 ml of THF was added a solution of t-
BuOK in THF (1.0 M, 60.0 ml) at 25 8C, giving a dark
green solution. [RhCl(cod)]2 (25.0 mg, 101 mmol) was
then added to the solution in one portion at 25 8C. After
stirring for 45 min at this temperature, 30 ml of hexane
(degassed by bubbling a dry nitrogen gas over 30 min)
was added to give greenish precipitates. The precipitates
were collected by filtration and washed thoroughly with
ether, hexane, and water, then dried in the air over night
to afford 57.0 mg (47.9 mmol, 93% yield) of the rhodium
H/27
103Rh: 1174.11678%.
/
complex 2 as a dark green solid (ꢀ95% purity in HPLC
/
and 1H-NMR analysis). IR (powder) 3025 (w), 2873 (w),
2829 (w), 1600 (w), 1493 (w), 1455 (w), 1430 (w), 1189
(w), 1152 (w), 1100 (w), 1084 (w), 1075 (w), 1063 (w),
1030 (w), 851 (m), 759 (m), 741 (s), 724 (m), 699 (s); 1H-
3.5. Synthesis of (h,2h2-1,4-cyclooctadiene)-
[(1,6,7,8,9h)-10,22,25-triphenyl-22,25-dihydro(C70-
D
5h(6))[5,6]fulleren-7(10H)-yl]rhodium(I)
ŽRh(C70Ph3)(cod) (4)
NMR (CS2, 400 MHz) d 2.22Á
CHCH2), 2.50Á2.72 (m, 6H, CHÄ
Jꢀ12.4 Hz, 1H, PhCHH), 4.19 (d, Jꢀ
PhCHH), 4.65Á4.73 (m, 2H, CHÄ
Hz, 1H, PhCHH), 4.84 (d, Jꢀ13.2 Hz, 1H, PhCHH),
5.40Á5.48 (m, 2H, CHÄCH), 7.37Á7.57 (m, 4H, Ph),
7.67Á7.75 (m, 5H, Ph), 7.85 (t, Jꢀ7.8 Hz, 2H, Ph), 7.94
(d, Jꢀ7.2 Hz, 2H, Ph), 8.35 (d, Jꢀ7.2 Hz, 2H, Ph);
/
2.32 (m, 2H, CHÄ
/
/
/
CHCH2), 4.05 (d,
This compound was synthesized in the same manner
as 2. Starting from 49.8 mg of C70Ph3H (46.4 mmol),
56.1 mg of 4 (43.8 mmol, 94% yield) was obtained as a
/
/
12.4 Hz, 1H,
/
/
CH), 4.74 (d, Jꢀ13.2
/
/
dark green solid (ꢀ
95% purity in HPLC and 1H-NMR
/
/
/
/
analysis). IR (powder) 3059 (w), 3027 (w), 2914 (w),
2872 (w), 2837 (w), 1492 (m), 1456 (s), 1446 (m), 1126
(m), 1074 (w), 1034 (s), 943 (w), 863 (m), 792 (m), 748
/
/
/
/
13C-NMR (CS2, 100 MHz) d 31.10, 33.63, 47.99, 53.94,
57.24, 58.75, 59.83, 74.73, 74.92, 127.43, 127.88, 127.99,
128.24, 128.39, 128.59, 128.93, 129.23, 129.25, 129.29,
130.08, 131.03, 131.20, 135.15, 135.47, 135.49, 135.57,
135.89, 139.54, 140.50, 142.37, 142.49, 142.50, 142.70,
142.79, 143.01, 143.12, 143.23, 143.28, 143.39, 143.75,
143.94, 144.00, 144.14, 144.36, 144.62, 144.75, 145.39,
145.43, 145.49, 145.51, 145.62, 146.45, 146.55, 146.72,
146.84, 147.01, 147.03, 147.08, 147.14, 147.20, 147.22,
148.26, 148.41, 148.43, 148.88, 149.12, 149.26, 150.14,
150.18, 156.63, 157.60; UV lmax 696, 379, 311 nm;
HRMS (APCI-) Found: 1190.14575; Calc. for C88-
(s), 694 (s); 1H-NMR (400 MHz, C6D6) d 1.34Á
/
1.39 (m,
1.74 (m, 4H, CH2), 3.43 (br s, 4H, CHÄ
6.97 (m, 6H, Ph), 7.32Á7.38 (m, 3H, Ph),
7.46 (m, 4H, Ph), 8.92Á
8.89 (m, 2H, Ph); 13C-
4H, CH2), 1.64Á
CH), 6.85Á
7.40Á
/
/
/
/
/
/
NMR (CS2/toluene-d8, 100 MHz) d 30.94, 56.90, 57.71,
71.76, 92.14, 100.23, 109.84, 129.25, 129.63, 129.89,
131.77, 131.87, 132.45, 132.88, 138.25, 139.89, 140.74,
142.80, 144.25, 144.43, 144.56, 144.65, 145.26, 145.78,
145.92, 146.22, 146.35, 146.59, 147.14, 147.34, 147.42,
147.54, 147.71, 147.85, 148.61, 148.97, 149.05, 149.54,
149.97, 150.97, 154.84, 157.75; HRMS (APCI-) Found:
1282.11576; Calc. for C96H/27
103Rh: 1282.11678%.
/
H/31
103Rh: 1190.14808%.
/
3.4. Synthesis of [(1,2,3,4,5-h)-6,9-dibenzyl-12-phenyl-
9,12-dihydro(C60-Ih)[5,6]fulleren-1(6H)-yl](h2,h2-
norbonadiene)rhodium(I) ŽRh[C60(PhCH2)2Ph](nbd)
(3)
3.6. General procedure of alkyne trimerization reaction
catalyzed by 2
To a degassed solution of 2 (4Á8 mmol) in 1,2-
/
dichlorobenzene was added an alkyne substrate (0.8
mmol) in one portion at ambient temperature and
This compound was synthesized in the same manner
as 2. Starting from 21.0 mg of 1 (21.4 mmol), 24.2 mg of
the resulting mixture was heated at 60Á100 8C. The
/
3 (20.6 mmol, 96% yield) was obtained as a dark green
reactions were monitored with TLC as well as HPLC
(Buckyprep column), indicating the reactions were
1
96% purity in HPLC and H-NMR analysis).
solid (ꢀ
/
IR (powder) 3060 (w), 3027 (w), 2917 (w), 1600 (m),
1493 (m), 1453 (w), 1030 (m), 739 (m), 697 (s); 1H-NMR
stopped after 1Á3 days. After cooling, the reaction
/
mixture was diluted with toluene and purified by flash
column chromatography to give a trimerization product
together with the recovered starting material (if any).
(CS2, 400 MHz) d 1.63Á
/
1.67 (m, 2H), 3.86Á/3.98 (m,
4H), 4.02Á4.10 (m, 2H), 4.73Á
/
/
4.78 (m, 2H) 4.65 (d, Jꢀ
/

M. Toganoh et al. / Journal of Organometallic Chemistry 683 (2003) 295Á
/
300
299
Table 2
Crystal data and data collection parameters of 4×
Hydrogen atoms were placed at calculated positions (CÃ
/
˚
/CS2
Hꢀ
/
0.95 A) and kept fixed. In the subsequent refine-
ment, the function av(F2oꢂ
/
F2c)2 was minimized, where
Complex
Formula
Rh(C70Ph3)(cod)×CS2
/
jFoj and jFcj are the observed and calculated structure
factor amplitudes, respectively. The agreement indices
C97H27RhS2
1359.32
Monoclinic
P21/n
Formula weight
Crystal system
Space group
are defined as R1ꢀ
/
a(jjFojꢂ
/
jFcjj)/ajFoj and wR2ꢀ
/
[av(Fo2ꢂF2c)2/a(vFo4)]1/2. Since Rh[C70Ph3(cod)] mole-
/
˚
a (A)
10.257(3)
17.780(4)
29.447(5)
90
cule was positionally disordered, R indices of this
analysis were not ideal, but the structural data were
judged to be reliable enough for confirmation of the
structure assigned by the spectroscopic methods.
˚
b (A)
˚
c (A)
a (8)
b (8)
94.110(14)
90
g (8)
3
V (A )
˚
5356(2)
4
1.667
Z
Dcalc (g cmꢂ3
F(0 0 0)
Temperature (K)
)
4. Supplementary material
2660
153(2)
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 209668 for complex 4. Copies
of this information can be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
Crystal size (mm)
2umin, 2umax (8)
Number of reflection measured (Total)
0.30ꢁ
4.8, 51.2
9791
/
0.10ꢁ0.02
/
Number of reflection measured [I ꢀ
Number of variables
R1, wR2 (all data)
/
2.0s(I)] 5501
1021
0.2126, 0.4106
0.1447, 0.3668
1.34
1EZ, UK (Fax: ꢃ44-1223-336033; e-mail: deposit@
/
R, Rw [I ꢀ
/
2.0s(I)]
Goodness-of-fit on F2
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
This study was supported by a Grant-in-aid for
Scientific Research (Specially Promoted Research) and
by the 21st Century COE Program for Frontiers in
Fundamental Chemistry from the Ministry of Educa-
tion, Culture, Sports, Science and Technology. M.T.
thanks JSPS for a predoctoral fellowship.
3.7. Hydroboration reaction catalyzed by 2
A solution of 4-(benzyloxy)cyclohexene (49 mg, 0.26
mmol) and 2 (5.3 mg, 4.4 mmol, 1.7 mol.%) in 2.5 ml of
THF was degassed with freezeÁthaw cycles 3 times. To
/
this solution was added catecholborane (100 ml, 0.94
mmol, 3.6 equivalent) at 25 8C and the resulting mixture
was stirred at this temperature for 3 d. The reaction
mixture was treated with MeOH (1 ml), aq. NaOH (2 N,
1 ml) and H2O2 (35%, 1 ml), and extracted with ether.
The extracts were washed with aq. NaOH and brine,
dried over anhydrous MgSO4, filtered and evaporated to
give a crude product. Purification was achieved by flash
column chromatography to give hydroboration pro-
ducts as a mixture of four isomers. The isomeric ratio
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355;
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/
Ka (graphite monochro-
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/
statistics are summarized in Table 2. The structure was
solved by the direct method (SHELXS-97) [13] and
expanded using Fourier techniques (DIRDIF-94) [14].
The non-hydrogen atoms were refined anisotropically
by the full-matrix least-square method (SHELXL-97) [13].
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Nakamura, J. Organomet. Chem. 599 (2000) 32;
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